In known linear adjusting devices for great adjusting paths, the bearing elements between the adjusting body and the carrier body are formed as roll bodies. However, roller bearings of this type are not satisfactory for very small adjusting steps in the range of some micrometers, since the friction borne within them results in inaccurate adjustment as well as in uneven adjusting movement. Further to this, roller bearings used in linear adjusting devices are sensitive to dust and other contaminations, are subject to wear and they necessitate some kind of lubrication. With these features, difficulties have to be encountered especially under special environmental circumstances, such as extremely high or low temperatures, under vacuum conditions and agressive atmosphere etc.
However, also linear adjusting devices of the present kind are known (DE-review "VDI-Zeitschrift", Vol. 83, 1939, No. 45, p. 1194, 1195) in which the bending springs are arranged in such a way that the longitudinal direction of their U-legs extends perpendicular with respect to the adjusting path and that the adjusting movement occurs against the spring force. In this way, a simple parallel guide of the adjusting body is possible which, however, is suitable only for short adjusting paths. Further, the adjusting body has to be held against the forces of the bending springs in all its positions outside the balance position of the spring.
Further, a table is known (DE-AS 2440088) which can be two-dimensionnally adjusted within the micrometer range by means of four groups of bending springs, each group comprising two leaf springs bent into U-shape and being located in pairs at the opposite table sides in such a way that the plane of the U-legs of the leaf springs extends perpendicular with respect to the plane of the table and the longitudinal direction of the U-legs of the leaf springs extends along the respective table side. At each of two adjacent table sides an electro magnet is arranged as an adjusting drive which can be adjusted with respect to its magnetic force. Thereby, the table can be displaced according to the adjusted magnetic force of the electromagnets, staggered by 90.degree., in each direction within the plane of the table until the equilibrum between the magnetic forces and the springs forces of the leaf springs is reached. Also by this adjusting device only short adjusting paths can be achieved and the adjusting movement occurs against the spring force of the leaf springs.
The main objects of this invention are to provide a linear adjusting device of the type specified in the introductory part, which especially can also be used under extreme environmental circumstances, e.g. at cryogenic temperatures and under vacuum conditions, and which renders possible an adjustment nearly without friction, furthermore, which has a great guiding accuracy on long adjusting paths, works for a long durability practically without maintenance and is in principle adapted--in spite of the long adjusting path--for adjusting steps within micrometers as well as for very slow, stable and very smooth adjusting movements.
According to the improvement in the present invention, the U-legs of each of the bending springs extend longitudinally along the adjusting path, and the bending springs of at least one of said groups of bending springs are arranged in such a way that the vertex lines of their U-bends--when seen in a cross section being perpendicular to said adjusting path--extend at oblique angles to the vertex lines of the U-bends of the bending springs of another group of bending springs.
In the linear adjusting device as in this invention, the U-bend of the strip-like bending springs fixed in U form will be displaced along its longitudinal direction as a chain track or caterpillar band during the adjustment motion of the adjusting device.
For this, one of the U-legs of the bending spring will become shorter in the course of the displacement and the other one will become longer. In this way, only an elastic deformation of the bending springs occurs in the course of the adjustment of the adjusting body, and there is no friction at the U-bend during the displacement. Further, the adjusting motion of the adjusting body is directed perpendicular to the spring forces of the bending springs. Accordingly, no spring force of the bending springs acts against the adjusting motion.
Since an inner friction within the bending springs will not be borne until the bending flexibility of the bending springs is not exceeded, it is possible to provide an adjusting device according to this invention which has a very easy and smooth running assuming a proper bending flexibility of the springs. This fact remains also true when the adjusting device is operated at cryogenic temperatures at which, indeed, the coefficient of elasticity will generally be greater, but which is expedient for the rigidity of the bearing.
As it is already mentioned, the adjustment of the adjusting body arises from the chain track like displacement of the U-bends of the bending springs which can be realized in very small adjusting steps. Thus, the linear adjusting device according to this invention is especially adapted for very small adjusting steps being in the range of e.g. some micrometers. At the same time, adjusting steps in the range of some decimeters are possible, too. Further to this, the linear adjusting device is suitable for extremely slow and steady adjusting speeds in the range of e.g. some micrometers per second on the base of the deformation mechanism of the bending springs achieved in this invention.
Furthermore, the adjusting device according to this invention needs no lubrication and, thus, it can be used not only at the lowest temperatures but under other extreme conditions, too, such as high vacuum or high temperatures. Moreover, the adjusting devices as in this invention works with stable effect independently from heat dilatation and is not sensitive against contaminations since the deformations of the bending springs will not be effected by contaminants.
The bending springs arranged according to the invention take charge of the supporting as well as guiding of the adjusting body, and the guiding forces are transmitted in a cross sectional direction being perpendicular to the direction of bending of the springs, i.e. to the direction in which the ends of the springs are bended towards each other for having the U-like form. In this cross sectional direction, the springs have, in relation to the bending direction, a greater rigidity because of having a greater width than thickness. Further to this, the guiding forces are distributed under the springs having identical measurements in a uniform manner.
Since in every group of bending springs, more than one bending springs are arranged one behind the other parallel to the adjusting path, they counteract to angle deflections of the adjusting path and parallel to the bending direction of the springs. Nevertheless, the springs of at least one group of bending springs are arranged, in respect to the springs of another group of bending springs, under oblique angles when seen in cross section, thus, to these angle deflections will also be counteracted.
Taken as an example, three groups of bending springs can be provided, two of which are arranged on both sides of the adjusting path in a manner, that the vertex lines of the U-bends of the bending springs of these two groups of bending springs will pass vertically. The third group of of bending springs is arranged in the middle between these two groups of bending springs in a manner that the vertex lines of the U-bends of their bending springs will pass horizontally.
However, preferably, the groups of bending springs are distributed between the adjusting body and the carrier body in a way, that they will be located on the sides of an imaginery polygon when seen in a cross section of the adjusting body and the carrier body perpendicular to the adjusting path, and the number of corners of the polygon will correspond to the number of groups of bending springs. As a result of this arrangement of bending springs around the adjusting body, the torsional rigidity of the support of the adjusting body will be enlarged and a stable guidance will be reached.
It is further preferred to arrange four groups of bending springs between the adjusting body and the carrier body along the sides of a rectangle seen in a cross section being perpendicular to the adjusting path and which groups have an angle of 45.degree. in respect to the vertical also seen in this cross section. In this way, the bending springs having identical measurements cooperate in the guidance as well as in the support of the adjusting body.
For the band-like bending springs, the requirements of having small resistance to bending in the sake of a small bending radius and, thus, a compact structure as well as of having a highest possible cross rigidity for transmitting high guidance and support loads exist. With metallic constructions materials preferred as materials of the bending springs, the small resistance to bending can be reached by an as small thickness of the springs as possible. With this, however, the torsional rigidity of the bending springs will also be smaller resulting in a smaller cross rigidity of the bending springs. For reaching a great cross rigidity with this bending springs, cross ribs being perpendicular to the adjusting path are arranged on the whole free length of the band-like bending springs in an equdistantial manner. In this way, torsion of the bending springs can occur only on the areas without reinforcement between the cross ribs and, thus, the cross rigidity will be determined by the arrangement and the number of cross ribs.
The cross ribs are made as solid ribs and they can have a half-circular or a triangular or, especially, a rectangular form. With this, it is possible to form the cross ribs only on one side of the bending springs, especially on the inner surface of the U-bends of the bending springs. For a still greater cross rigidity, it is preferred to provide a great number of this cross ribs on both sides of the band-like bending springs, wherein the cross ribs on one side of the bending springs coincide with those on the other side or the cross ribs on one side of the bending spring are staggered in respect to the cross ribs on the other side, a small distance is left free.
The bending radius of the U-bends of the bending springs are chosen to permit only elastical deformation of the bending springs, thus, inner friction on the basis of plastical deformation of the bending springs will not arise.
In the most preferred case the bending springs can be formed as rectangular leaf springs. However, it is also possible to make them of parallel bands arranged side by side spaced somwhat apart and connected to each other by e.g. the cross ribs for having the springs a ladder-like form.
In the adjusting device according to this invention, it is also possible to arrange more than one bending springs as in this invention in side by side relationship. Further to this, a substantial freedom is given for the relative positions of the groups of bending springs to each other. They can have a smaller as well as a greater distance between them according to the given requirements of the adjusting body. The adjusting body can be a pointer of a measuring instrument, a core of a solenoid or another adjusting member. Furthermore, the adjusting body may be a means carrier having a rod-like or plate-like or another shape.
In all groups of bending springs, at least two bending springs arranged according to the invention are provided. The U-bends of the bending springs in the groups of bending springs may point in the same direction or they may be turned away from each other. Preferably, however, the U-bends of the bending springs in the groups of bending springs are turned towards each other and, thus, the distance between their fixing points on the adjusting body and the carrier body, respectively, is great.
The bending springs between the adjsuting body and the carrier body are arranged in such a way that the vertices of the U-bends are aligned perpendicular to the adjusting path in all adjusting positions of the adjusting body. Further to this, it is also possible in the adjusting device according to this invention to arrange the bending springs between the adjusting body and the carrier body in a manner that they do not touch the adjusting or carrier bodies, respectively, expect at the ends of the spring, at which the springs are fixed on the on the adjusting body and the carrier body, respectively. However, lay-down tracks for the U-legs of the springs may be provided on the adjusting body and the carrier body along the adjusting path wherein a lay-down track of the adjusting body forms with another lay-down track of the carrier body a pair of lay-down tracks. Between the lay-down tracks of this pair of lay-down tracks, one group of bending springs is arranged, the U legs of which lie on the respective lay-down track. In this embodiment, this results in the fact that during the adjustment, the U leg getting longer by running out of the U-bend of the bending spring is laid down onto the associated lay-down track and the other U leg getting shorter by running into the U-bend of the bending spring is lifted off the associated lay-down track. By leaning the U legs of the bending springs against the lay-down tracks, the accuracy of guidance can additionally be improved.
The surface lines passing planewise perpendicularly to the adjusting path of each of the lay-down tracks are stright lines being parallel to each other. However, the lay-down tracks need not to be straight and parallel ones to the adjusting path along it, only it has to be provided that the bending springs unrolling on the lay-down tracks will placed always be perpendicular to the adjusting path. However, it is more preferable that the lay-down tracks run in parallel to the adjusting path and the lay-down tracks of each pair of lay-down tracks are parallel to each other.
As it is already mentioned, the adjusting device in this invenion is especially adapted for achieving small adjusting steps, for the purpose of which a properly controlled adjusting drive may be provided. However, it has been found that longitudinal oscillations of the adjusting device of this invention may occur, especially with slow adjusting motions. With respect to this, it is proposed in another embodiment of this invention to use an electromechanical linear motor as adjusting drive being controlled with active oscillation absorption. The main idea of such types of control is per se well known, e.g. for active electromagnetic bearings. In this, it will be actively counteracted to the oscillations by producing counterforces through the control which absorb the oscillations of the adjusting member. Especially through this kind of active oscillation absorption of the linear motor, the adjusting accuracy within some micrometers and the extremely slow and stable adjusting speeds of the adjusting device according to this invention can be reached. Because of this, it is also important to guide the linear motor's slide fixed or attached to the adjusting body without friction and, thus, to avoid an influence of the guidance or bearing of the slide of the linear motor on the friction-free guidance of the adjusting body.